1. Field of the Invention
The present invention is generally related to a fuel or air-fuel injector and, more particularly, to a fuel injector made with a poppet that is formed of a material that increasingly conforms in shape to an associated valve seat in response to continued wear of the poppet through repeated contact with the valve seat.
2. Description of the Prior Art
Many different types of fuel injectors are known to those skilled in the art. Certain types of fuel injectors operate at high fuel and air pressures in order to be able to inject a fuel/air mixture directly into a combustion chamber of an internal combustion engine. Other types of fuel injectors operate at lower pressures and inject a fuel mist into an air stream flowing to combustion chambers of an internal combustion engine.
U.S. Pat. No. 5,090,625, which issued to Davis on Feb. 25, 1992, describes nozzles for in-cylinder fuel injection systems. The nozzle has a body having a fuel passage terminating in a port that, in use, communicates the fuel passage with an engine combustion chamber. The port has an annular seat therein and a valve element also having an annular seat which cooperates with the seat in the port to control fuel flow therein. An annular flow directing surface extends downstream from each of the annular seats, and each flow directing surface is contoured to blend smoothly with its respective seat.
U.S. Pat. No. 5,685,492, which issued to Davis et al on Nov. 11, 1997, describes fuel injector nozzles. An engine fuel injector has a selectively openable nozzle through which a fuel is delivered to the combustion chamber of the engine. The nozzle comprises a port having an internal annular surface and a valve member having an external annular surface coaxial with respect to the internal annular surface. Sealing contact between the valve member and the port is provided therebetween along a circular seat line substantially coaxial to the respective annular surfaces. The annular surfaces are configured so that when the internal and external annular surfaces are in sealing contact along the circular seat line, the seat line is located adjacent the downstream end of the passage for delivery of fuel with respect to the direction of the flow of fuel through the passage. The maximum width of the passage between the annular surfaces is not substantially more than 30 microns.
U.S. Pat. No. 6,047,671, which issued to Tubb et al on Apr. 11, 2000, describes a fuel injector system for an internal combustion engine. More particularly, a method of lubricating and cleaning a fuel injector of a fuel injection system of an internal combustion engine during running of the engine includes delivery both a lubricant and a cleaning additive to the injector. The injector injects directly into the combustion chamber of the engine. The lubricant and cleaning additive are delivered to the fuel exit area of the injector.
U.S. Pat. No. 4,817,873, which issued to McKay on Apr. 4, 1989, describes nozzles for in-cylinder fuel injection systems. A fuel injection nozzle for use in direct injection of fuel to an internal combustion engine is described in which the injector nozzle comprises a body having a longitudinal fuel passage terminating in a port which in use communicates the fuel passage with the combustion chamber of the engine. A valve element to co-operate with a valve seat provided in the port to control fuel flow to the combustion chamber and a fuel spray directing surface in the port extending downstream from the valve seat are described. The body includes a cavity between the spray directing surface and that part of the body through which the fuel passage passes, with the cavity being shaped and located to restrict the area for conductive heat flow from the spray directing surface to fuel passage area of the body. The restriction of the heat flow maintains the spray directing surface at a temperature to combust particles of combustion products deposited thereon.
U.S. Pat. No. 5,119,792, which issued to Gu on Jun. 9, 1992, describes an electromagnetic fuel injector with central air blow and poppet valve. The fuel injection mechanism for a two-stroke engine has two valve assemblies controlled by two solenoid assemblies. One solenoid assembly is provided for controlling the quantity of fuel to be injected into the fuel chamber and the other solenoid assembly includes a main solenoid for controlling the opening of a main fuel injection valve at an appropriate time, whereby fuel pre-stored in the fuel chamber is atomized and injected by a flow of high pressure air. The main fuel injection valve is formed in mushroom shape, wherein its middle portion is hollow and provides a passage for compressed air. The flow of compressed air, in two streams, is used for the solenoid head injection to improve an injection spray effect, to shorten the time of cleaning the fuel injector and to simplify the structure.
U.S. Pat. No. 5,407,13 1, which issued to Maley et al on Apr. 18, 1995, describes a fuel injection control valve. The control valve assembly for a fuel injector includes a valve seat with fluid inlet and fluid outlet and a flat seating surface. A poppet valve has a concave end portion with a knife edge for sealingly engaging the flat seating surface on the valve seat. The poppet valve is operated to close by a solenoid coil and is opened and maintained open by a return spring or a permanent magnet. Faster valve closing and faster valve opening is obtained.
U.S. Pat. No. 5,947,380, which issued to Coldren et al on Sep. 7, 1999, describes a fuel injector utilizing flat-seat poppet valves. A fuel injector includes a center tube, a first valve separate from the center tube and surrounding a first end of the center tube and a second valve also separate from the center tube and surrounding a second end thereof. A solenoid is actuable to independently move the first and second valves and thereby control the application of fluid pressures to first and second ends of a check assembly, in turn to control injection of fuel into an associated engine cylinder.
The patents described above are hereby explicitly incorporated by reference in the description of the present invention.
Poppets made in accordance with techniques known to those skilled in the art exhibit certain disadvantages under certain conditions. For example, when operated in severely corrosive environment, such as sea water applications, even poppets that are made of stainless steel material can corrode. When combined with certain other stress increasing conditions, this corrosion can lead to failure of the structural integrity of the poppets. This failure can, in turn, lead to the separation of the valve head of the poppet from the stem portion of the poppet. When this occurs, the valve head can fall into the combustion chamber and result in severe damage to the engine. Another problem that occurs in conjunction with poppets made in accordance with the prior art is that the wear surfaces of the poppet can exhibit microscopic chipping and cracking. If this occurs, the chipped area can allow leakage of fuel around the valve head of the poppet. In order to improve the wear resistance characteristic of the poppet, techniques known to those skilled in the art typically attempt to provide a hard surface in order to resist wear. The attempts to achieve higher Rockwell C hardness values in order to withstand the rigorous contact experienced by valve heads of poppets often include the addition of carbon to the stainless alloy used to make the poppet. The carbon combines with other alloying elements present in the stainless steel and forms primary carbides in the material. While improving the hardness, strength, and wear resistance of the material, the presence of alloy carbon levels in the stainless steel and the resulting existence of primary carbides lead to lower salt water corrosion resistance and a certain degree of brittleness that can result in microscopic chipping and cracking at the wear surface. It would therefore be significantly beneficial if a poppet could be made in such a way that the poppet material exhibited a high degree of salt water corrosion resistance and, in addition, resisted chipping and cracking at the wear surface.
A fuel injector made in accordance with the preferred embodiment of the present invention comprises an actuator portion and a nozzle portion having a fluid conduit extending there through and a valve seat formed in association with the fluid conduit. In addition, the fuel injection made in accordance with the present invention comprises a poppet having a valve head shaped to be received by the valve seat in sealing relation, the poppet being moveable relative to the nozzle portion between a closed position in which the fluid conduit is blocked and an open position in which the fluid conduit is at least partially unblocked, with the valve head of the poppet having a Rockwell C hardness value of less than 50.
One embodiment of the present invention comprises a valve head which is made of a martensitic stainless steel having an alloy carbon level of less than 0.5% and, more particularly, a valve head that is made of a material which is, by weight, between 12.25% and 13.25% chromium, between 7.5% and 8.5% nickel, between 0.9% and 1.35% aluminum, less than or equal to 0.5% carbon, and between 2.0% and 2.5% molybdenum.
A valve head made in accordance with the present invention is made of a material which is generally free of primary carbides. One embodiment of the present invention comprises a valve head which is made of a material which is precipitation hardenable stainless steel. The valve head of the present invention is conformable by wear with the valve seat in order to result in a generally smooth and chip free surface of the valve head in response to repeated contacts between the valve head and the valve seat.
A particularly preferred embodiment of the present invention is made of a material selected from the group consisting of martensitic stainless steel having an alloy carbon level less than 0.5% and precipitation hardenable stainless steel. The actuator can be a solenoid which is electrically actuable. Alternative embodiments of the present invention can incorporate a hydraulic actuator. The poppet is axially moveable within the fluid conduit in response to the actuator portion of the fuel injector, in a preferred embodiment of the present invention. After repeated contacts between the valve head and the valve seat, a valve head made in accordance with the softer material of the present invention has a significantly improved (i.e. smoother) surface finish in the region of contact with the valve seat.